BUSINESS SEGMENT INFORMATION - Additional Information (Details) - segment	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Number of reportable segments	2
Percentage of sales to major customers	10.00%
AB Volvo
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage of sales to major customers	22.00%	23.00%	24.00%
Daimler AG
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage of sales to major customers	17.00%	18.00%	20.00%
PACCAR
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage of sales to major customers	10.00%	9.00%	6.00%
Navistar
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage of sales to major customers	9.00%	9.00%	11.00%